The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
FIG. 1 shows a hard disk drive (HDD) 10 that includes a hard disk assembly (HDA) 12 and a HDD printed circuit board (PCB) 14. The HDA 12 includes one or more platters 16, which have magnetic surfaces that are used to store data magnetically. Data is stored in binary form as a magnetic field of either positive or negative polarity. The platters 16 are arranged in a stack. The platters and/or the stack is rotated by one or more spindle motors (one spindle motor 18 is shown). One or more read/write heads (hereinafter, “heads”) read data from and write data on the magnetic surfaces of the platters 16. A single head 20 is shown. Each of the heads includes a write element (e.g., an inductor) that generates a magnetic field and a read element (e.g., a magneto-resistive (MR) element), which senses the magnetic field on one of the platters 16. The heads are mounted at a distal end of one or more actuator arms (a single actuator arm 22 is shown). An actuator, such as a voice coil motor (VCM) 24, moves the actuator arm 22 relative to the platters 16.
The HDA 12 includes a preamplifier device 26. The preamplifier device 26 may include amplifiers for amplifying signals received from the heads. When reading data, generated magnetic fields induce low-level analog signals in the read elements of the head 20. The amplifiers amplify the low-level analog signals and output amplified analog signals to a read/write (R/W) channel (hereinafter, “read-channel”) module 28.
The HDD PCB 14 includes the read-channel module 28, a hard disk controller (HDC) module 30, a processor 32, a spindle/VCM driver module 34, volatile memory 36, nonvolatile memory 38, and an input/output (I/O) interface 40. During write operations, the read-channel module 28 may encode the data to increase reliability by using error-correcting codes (ECC) such as run length limited (RLL) code, Reed-Solomon code, etc. The read-channel module 28 then transmits the encoded data to the preamplifier device 26. During read operations, the read-channel module 28 receives analog signals from the preamplifier device 26. The read-channel module 28 converts the analog signals into digital signals, which are decoded to recover the data previously stored on the platters 16.
The HDC module 30 controls operation of the HDD 10. For example, the HDC module 30 generates commands that control the speeds of the one or more spindle motors and the movement of the one or more actuator arms. The spindle/VCM driver module 34 implements the commands and generates control signals that control the speeds of the one or more spindle motors and the positioning of the one or more actuator arms. Additionally, the HDC module 30 communicates with an external device (not shown), such as a host adapter within a host device, via the I/O interface 40. The HDC module 30 may receive data to be stored from the external device, and may transmit retrieved data to the external device.
The processor 32 processes data, including encoding, decoding, filtering, and/or formatting. Additionally, the processor 32 processes servo or positioning information to position the heads over the platters 16 during read/write operations. Servo, which is stored on the platters 16, ensures that data is written to and read from correct locations on the platters 16. In some implementations, a self-servo write (SSW) module 42 may write servo on the platters 16 using the heads 20 prior to storing data on the HDD 10.
To increase the amount of data storage on a platter, densities of tracks (amounts of data stored in predetermined surface areas) are increasing, widths of tracks are decreasing, and pitches of tracks (or distances between tracks) are decreasing. As a result, a width of a head can be wider than a width of a single track. Because of this relationship between the head and the track, the head can pick up inter-track noise. Inter-track noise can refer to magnetic field characteristics detected and associated with one or more tracks adjacent to the track being read.
The HDA 12 may include a two-dimensional magnetic recording (TDMR) system 50 having a trace suspension assembly (TSA) 52. The TSA 52 refers to the one or more actuator arms and transmission lines (e.g., transmission lines 54 are shown) extending between the preamplifier device 26 and the heads. The transmission lines (sometimes referred to as traces) are suspended over the platters 16 via the one or more actuator arms. A TDMR system, such as the TDMR system 50, uses multiple heads positioned adjacent each other to read a single track on a surface of a platter. Signals from the heads are processed to counteract, cancel and/or minimize noise (e.g., inter-track noise) detected during the reading of the track. This improves a signal-to-noise ratio for improved recovery of data stored on the track.
FIG. 2 shows a TDMR system 60 that may be used in the HDA 12 of FIG. 1. The TDMR system 60 includes read elements 62, transmission lines 64, and a preamplifier device 66. The preamplifier device 66 includes differential amplifiers 68. Each of the read elements 62 is connected to a respective one of the differential amplifiers 68 and a respective pair of the transmission lines 64. The read elements 62 are isolated from each other. Since the read elements 62 are isolated from each other, noise coupling between the read elements 62 and cross-couplings of signals detected by the read elements 62 is minimized. As a result, inter-head modulation of signals is insignificant. The differential amplifiers 68 provide differential output signals Out1, Out2. Gain of each of the differential amplifiers 68 may be adjusted to increase amplitudes of the output signals Out1, Out2 and/or to improve corresponding signal-to-noise ratios.